by Westructure the Timber Frame Kit company.

1. This Wood Information offers guidance for building surveyors and professionals in the construction industry who may need to survey timber framed houses. In this sheet, timber frame refers to buildings constructed from loadbearing panels comprising a framework of timber studs (usually softwood) covered with a wood-based board sheathing and lined internally, usually with plasterboard. Themal insulation is normally incorporated in the cavity between the studs.
   The external cladding is non-structural and may be self supporting masonry or lightweight materials which are attached to the timber framing. It does not deal with surveying traditional large section timber framed structures – information on surveying these buildings is included.
   
   
2. Most timber frame buildings in the UK will have been constructed after the second world war. TRADA’s first publication on the subject was published in 1944. The basic form of construction has not changed radically, although increasing sophistication in performance and the introduction of new materials have brought detail changes over the years.
   
3. Recent innovations in timber frame include the use of Structural Insulated Panel Systems (SIPS). A brief description is included. New types of wood-based board materials continue to be developed. Those used for sheathing include plywood, oriented strand board (OSB) and some types of impregnated fibreboard. Flooring is most commonly softwood boards, plywood or chipboard. Structural timber engineered components are also now available including prefabricated I-joists, laminated veneer lumber (LVL) and parallel strand lumber (PSL).
   
4. Fungi can cause staining, decay and weakening of timber but cannot live in wood with a moisture content below 20%. In a well designed and maintained timber frame building the timber is kept well below this level and is therefore not at risk from decay. Moisture content readings above this level require further investigation to establish their cause. With its relatively cold temperate climate, structural timber in the UK is not generally at risk of significant damage from insect infestations. More information is available.
   
5. Professionals undertaking surveys of timber frame buildings should have an understanding of the overall design and typical detailing employed in this form of construction. Information is included in other Wood Information and in the Timber Frame Construction book. The approach to surveying a timber framed house is no different from that used for other methods of construction. There are many similarities with brick and block construction that can make timber framed houses hard to spot, but there are also tell-tale differences. This concentrates on details where timber frame construction differs enough from masonry to suggest specific checks. Establishing the reasons for apparent faults may demand a more rigorous investigation, such as using an endoscope to inspect cavities.
   
6. The local authority Building Control department is an obvious data source. It may have plans and details of a building’s construction method. Failing this a visual inspection, inside and out, may pick up on details typical of timber frame construction.
   
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   Timber Frame house building.
   
   
8. External visual inspection.
   In timber frame structures windows are fixed to the frame, not to the brickwork outer leaf. This may result in a deeper external reveal than is common with brick or blockwork construction. There should also be some indication of allowance for differential movement around the windows in brick- or block-clad timber frame houses.
9. Open perpends to allow cavity drainage and ventilation should be visible at the base of the external wall with weepholes over openings.
   
10. Internal visual inspection.
    The gable wall of a timber framed building will have a timber spandrel panel forming the gable panel (at roof level). On a party wall the panel will be clad with plasterboard. Note however, that if a party wall is brick or blockwork, other parts of the building’s structure could still be timber framed.
11. It may be possible to see the top of the timber wall panel at the eaves in the roof space. A timber structure will have the cavity closed by a timber batten or polythene-sleeved mineral wool cavity barrier.
    
    
12. In timber frame buildings the head binders or the top rail of the wall panels often have a planed finish. Their equivalent, the wall plates in masonry constructions are commonly left sawn. Typical dimensions of timber used in timber frame construction are 38 x 89 mm or previously imperial sizes of 3 x 2” or 4 x 2”. More recently, to accommodate additional thermal insulation, stud sizes have increased to 38 x 140mm.
    
    
13. On internal walls a metal detector or magnet may help locate the plasterboard fixing nails or screws. These give the position of supports, typically 400 mm or 600 mm centres, suggesting timber frame construction - although masonry cavity walls are now frequently dry lined with plasterboard on battens at similar centres. Note that metal foilbacked or metallised polyester film plasterboard render a metal detector useless.
    
    
14. Tapping on the wall above a window opening may distinguish between dry lining battens and a timber structure. Masonry with batten-mounted dry lining will sound hollow but timber frame will usually have a lintel immediately above the opening, so will sound solid. However, be aware that some timber framed systems incorporate the lintels higher in the wall in the header joist at the floor zone level.
    
    
15. On an external wall, by removing the cover plate to a light switch or power socket outlet (with the electricity supply isolated first) it may be possible to see the wall’s material. With timber frame you are likely to see a polythene vapour control layer, insulation partly or fully filling the void, backed by a wood-based board sheathing of plywood or OSB.
    
    
16. In an upper floor, inspect the end of a joist by lifting a floorboard or service trap near an external wall. If the joist is supported on timber rather than on brick or blockwork, the building is timber-framed.
    
17. Information continued on next page.